Chapter 8 Covalent Bonding 8.1 Molecular Compounds 8.2 The Nature of Covalent Bonding 8.3 Bonding Theories 8.4 Polar Bonds and Molecules Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

CHEMISTRY & YOU How are atoms joined together to make compounds with different structures? Although the types of pieces are limited, you can make many different toy models depending on how many pieces you use and how they are arranged. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds What information does a molecular formula provide? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds In nature, only the noble gas elements, such as helium and neon, exist as uncombined atoms. They are monatomic; that is, they consist of single atoms. Helium, which is less dense than air, is often used to inflate balloons. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds But not all elements are monatomic. O2 represents two oxygen atoms that are bonded together. Scuba divers breath compressed air, a mixture that contains oxygen gas. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Ionic compounds are generally crystalline solids with high melting points. Other compounds, however, have very different properties. Water (H2O) is a liquid at room temperature. Carbon dioxide (CO2) and nitrous oxide (N2O) are both gases at room temperature. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds The attractions that hold together the atoms in O2, H2O, CO2, and N2O cannot be explained by ionic bonding. These bonds do not involve the transfer of electrons. Ionic bond= transfer of electrons from one element to another Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Sharing Electrons Recall that ionic bonds form when the combining atoms give up or accept electrons. Another way that atoms can combine is by sharing electrons. Atoms that are held together by sharing electrons are joined by a covalent bond. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Sharing Electrons A molecule is a neutral group of atoms joined together by covalent bonds. Oxygen gas consists of oxygen molecules; each oxygen molecule consists of two covalently bonded oxygen atoms. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Sharing Electrons An oxygen molecule is an example of a diatomic molecule—a molecule that contains two atoms. Other elements found in nature in the form of diatomic molecules include hydrogen, nitrogen, and the halogens. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Sharing Electrons Molecules can also be made of atoms of different elements. A compound composed of molecules is called a molecular compound. Water is an example of a molecular compound. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Representing Molecules A molecular formula is the chemical formula of a molecular compound. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Representing Molecules A molecular formula shows how many atoms of each element a substance contains. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Representing Molecules The molecular formula of water is H2O. Notice that the subscript written after an element’s symbol indicates the number of atoms of each element in the molecule. If there is only one atom, the subscript 1 is omitted. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Representing Molecules A molecular formula reflects the actual number of atoms in each molecule. The subscripts are not necessarily the lowest whole-number ratios. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Representing Molecules Note that molecular formulas also describe molecules consisting of atoms of one element. For example, an oxygen molecule consists of two oxygen atoms bonded together; its molecular formula is O2. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Representing Molecules A molecular formula does NOT tell you about a molecule’s structure. In other words, it does not show either the arrangement of the various atoms in space or which atoms are covalently bonded to one another. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Representing Molecules A variety of diagrams and molecular models can be used to show the arrangement of atoms in a molecule. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Molecules and Molecular Compounds Representing Molecules The arrangement of atoms within a molecule is called its molecular structure. The molecular structure of carbon dioxide shows how the three atoms are arranged in a row. It also shows how the carbon atom in each molecule is in the middle between the two oxygen atoms. (Location) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Comparing Molecular and Ionic Compounds What representative units define molecular compounds and ionic compounds? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Comparing Molecular and Ionic Compounds The representative unit of a molecular compound is a molecule. For an ionic compound, the smallest representative unit is a formula unit. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Comparing Molecular and Ionic Compounds Recall that a formula unit is the lowest whole-number ratio of ions in an ionic compound. It is important not to confuse formula units with molecules. A molecule is made up of two or more atoms that act as a unit. No such discrete units exist in an ionic compound, which consists of a continuous array of ions. There is no such thing as a molecule of sodium chloride or magnesium chloride. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Comparing Molecular and Ionic Compounds Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds. Many molecular compounds are gases or liquids at room temperature. In contrast to ionic compounds, which are formed from a metal combined with a nonmetal, most molecular compounds are composed of atoms of two or more nonmetals. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Comparing Molecular and Ionic Compounds Water, which is a molecular compound, and sodium chloride, which is an ionic compound, are compared here. Array of sodium ions and chloride ions Collection of water molecules Formula unit of sodium chloride Molecule of water Chemical formula H2O NaCl Chemical formula Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Bonding and Interactions BIG IDEA Bonding and Interactions In molecular compounds, bonding occurs when atoms share electrons. In ionic compounds, bonding occurs when electrons are transferred between atoms. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.